Energy efficient engines of reduced size are desirable for fuel economy and cost reduction. Smaller engines provide less torque than larger engines. A supercharger assembly is sometimes used to increase the torque available from an engine. At low engine speeds, when higher torque is requested by a vehicle operator by depressing the accelerator pedal, the supercharger assembly provides additional air to the engine intake manifold, boosting air pressure and thereby allowing the engine to generate greater torque at lower engine speeds.
Assembling the supercharger assembly typically requires that a gap remain between the end faces of the rotors and an end portion or bearing plate of the supercharger housing in order to accommodate the stack-up of manufacturing tolerances of the components, as well as to accommodate thermal growth of the components that occurs during usage of the supercharger assembly. Leakage of air past the rotors, such as through the gap at the end faces, especially at low rotational speeds, can significantly reduce the ability of the supercharger assembly to provide engine boost.